Recording apparatus



Jan. 13, 1953 R; c. RUHLAND RECORDING APPARATUS 2 SHEETS-SHEET l Filed May 23. 1947 mM mL m i, ww m 3 N *www y vl) @www Jan. 13, 1953 Filed May 23. 1947 R. c. RUHLAND RECORDING APPARATUS I I I 2 SHEETS--SHEET 2 WMM Patented Jan. 13, 1953 UNITED STATES. PATENT OFFICE RECORDING APPARATUS" Roman C. Ruhland, Minneapolis, Minn., assignorvv to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delawaref Application May 23, 1947, Serial No; 749,957

17 Claims.

My invention relates to a multiple channel recorder which has unlimited application and which is especially applicable to usein' aircraft for lre cording on a'continuous record a plurality'of con- Y' ditions which Vare continually changing.

It is known vin the art of reccrding'devices to provide such systems with a balanceable net` Work such'as a Wheatstonebridge-a potentiometer circuit,"or the like.- Such systems are limited to a single bridge circuit for recordingqthel-variations in' asingle` condition,y or ay group'of bridge circuits each'of which are balanced within themselves to record a plurality of conditions It V;is` an object of this invention to providea system-y in which a plurality ci` potentiometersywhose effective values are 'varied by sensing elements, are

arranged" in the form of .a network so that they:

can be connected by \means of ya switching element toa balancing'potentiometer to form aplurality of electricallyconnected but individually balanceable bridge circuits.

It is also anobject -cf this invention to provide a system comprising a. plurality of bridges which can bel balancedby the same balancing potentiometer.

A lfurther object of this inventionis toprovide` a system which willgive instantaneous recordings of .a plurality ci fast..changingmagnitudes..

A still further .object .ci this invention. is to provide asi/stem in whichithe spacing 4 of the i recorded values on a single record sheet is divided into separate channels by ,virtueof .theelectrical values ofthe impedances of each .of v.the bridges without specic mechanicalrmeans .to.,so. posi. tion them.

other .object of .thisl invention visto provi-de a network .on .which the. records .oi some of :the bridges are spaced. inseparate channels across.

the vwidth of the record and the records of other of vthe bridges.v in the .networkare superimposed.,

upon the Vformer records .and expandedand oen.- teredwith respect to. the former records.

It is further an object-of this invention to provide an amplifier and relay. apparatus which iscperative lon receipt of signals from an as,-

sociated network in such Aa manner that one of the relays of said ampliierl and relai/#apparatus operates when a .signalof a particular phase is impressed upon the amplifier and the other relayn ofsaidamplier and relayapparatus operates whenv a signal vof the oppositesense is impressed upon the ampliiier, but both. remain .energizedduring the v`period when the phase of the signal.. changes,- as indicated by the balance pcintior.

the network, due to .timedelay means which are incorporated in each of therelays..

It is also an object .of this invention .to pro.` vide a system .which is small and compact and in which the-accuracy and. thereliability of the-v system is high.

Another object of` this invention. isprovided. in the system inwhichthespeed of rotation of the rotatingparts is reducedwith respect tothe rate of recording, thereby reducing the wearandpossibility of failure of the m'ovingparts.,

Various other objects, advantages and features of novelty which .characterize .my` invention are pointed out with particularity inthe claimsanneXed hereto and forminga part, hereof. How-- ever, for a better understanding of the invention, its advantages, and. objects attained by-its use, reference should be had to the subjoineddrawing, which forms a further part hereof and. to the accompanying-descriptive matter, in which I have illustratedand described certain preferred embodiments of my invention..

Figure .1 shows diagrammaticallyra preferred embodiment of a recordingisystem accordingto the invention together with an appertaining recording device. This system is .shown .for .con-

venience as .comprising six potentiometer sensing The .recording apparatus shovvnin Figure 1 a multiple channel flight recorderwhich will give. continuous record of. the variations in a pluralityA of...conditions.encountered during. flight.. rlhis apparatus comprises `anetvvork .unit I0,` an amplifier 2| and relay unit 22, anda recordingvunit 24 Whichare energized from' a common source .I I. The plurality of branches or. potentiometer legs IZ-I 1 of network unit I0 are connected in parallel with one another and also in parallel with a balancing variable impedance 20. As the balancing variable impedance 20 is continuously varied, it will sweep through during each revolution a balance point for each of the potentiometer legs |2--i1 or branches of the network unit l0. The output of the network unit is impressed upon the amplier 2l which in turn operates the relay unit 22. The relay unit 22 controls an inductive device energized from the D. C. source 23 to supply an electrical impulse to the recording unit 24 as the output of these network branches or legs I2-l1 are seouentially applied, as will later be described, to the amplier unit 2|. The recordinq unit 24 operates to record each of these balanced conditions of a continuously moving chart record in a manner which becomes apparent as the disclosure proceeds.

Network unit The network unit I0, as disclosed in Figure 1, is a compound impedance network comprising a plurality of parallel impedance or potentiometer legs l2-I1 which are connected in parallel with a balancing variable impedance 20. Potentiometer legs l2-l1 are connected by means of common conductors 34--35 to balancing variable impedance 20. The network is energized from a common source of power Il through transformer 21 whose secondary winding 3l is connected by means of conductors 32, 33 to potentiometer legs I2-i1. Primary winding 30 of transformer 21 is energized from source Il through conductors 25. 26. Each potentiometer or impedance leg I 2-l1 comprises fixed and variable resistances, as will be further described as the disclosure proceeds, connected in series with one another across the common conductors 34, 35. The variable resistances or potentiometers of these legs include fixed resistances and movable or wiping contacts which are operated by and insulated from sensing elements SI1- 51, SI1-G2. For simplicity, the sensing elements are shown in Figure 1 as coiled bimetallic strips. rlhe sensing elements are attached to the frame of the apparatus at the extremity opposite the contact bearing end in a manner to effect movement of the wiping contact along said potentiometers upon variation in temperature or other conditions affecting said sensing elements. The contacts of the variable resistances 'or notentiometers are connected, as will be noted below. to a switching unit 63.

Switchingf unit 63 comprises stationary contacts 65-10, 'in-12 and rotary wiping contact .B4 which is driven bv and insulated from shaft 8 4 of motor 85. Stationary contacts or elements 615-10. Til- .12 form an annular shaped stationary contact structure whose individual contacts or elements are separated from one another by pieces f insulating material. Each contact or element is in the form of approximately a 60 segment. Wiping contact 64 is pivoted from the center of this annular structure where it is mounted on shaft 84 and contacts each of said elements as the shaft is rotated. The number of stationary elements of switch S3 is directly related to the number of potentiometer legs in network I0 which are to be balanced by the balancing variable impedance 20. The rotating contact or wiper E4 is connected to balancing variable impedance 20 through am- Dlier 2| to complete the output circuits from potentiometer legsv I2--I1 to the balancing im- 4 pedance 20 in a manner which will become evident.

The balancing variable impedance 20 comprises an annular shaped potentiometer 8! whose resistance winding is continuous. Conductors 34, 35 are tapped to said winding at two taps spaced 180 apart. Variable impedance 20 also includes a wiper 82 which is driven by and insulated from shaft 84 of motor 85. Wiper 82 is connected to ground conductor 83 for the purpose of completing the output circuits of the network as referred to above.

In the network shown in Figure 1, six potentiometer legs or branches for a network were used merely for simplicity in disclosure. The number of potentiometer legs required in such a network is governed, theoretically, only by the number of conditions whose variations it is desred to separately record. The physical size of the balancing variable impedance 20 as well as its ohmic value, the number of stationary contacts of rotary switch 63 and the values of the fixed and variable resistances as well as their positioning with respect to one another in the potentiometer legs are all dependent upon the number 0f sensing elements or network branches used. Each potentiometer leg is effectively a variable resistance or potentiometer in which the movable portion or wiping contact is restricted to movement over a limited extent of that leg. The use of the fixed resistors merely facilitates the positioning of the variable resistance or the variable portion of the potentiometer leg along the extent of the potentiometer leg so that it can be made to correspond With a similar portion of the balancing variable impedance. Each leg then contains but one variable resistor or potentiometer from which a connection is made to a stationary element of the rotary switch. With the present network of six potentiometer branches or legs it is evident that each leg must be balanced within a denite 60 sector of the balancing Variable impedance winding 8i in order that all the network branches or legs lZ-i! be balanced in a single revolution of balancing variable impedance wiper 82. In accomplishing this, the variable resistance 0f each potentiometer leg must be spaced within the potentiometer leg in a position which corresponded with the 60 sector of the balancing variable impedance winding BI in which it was to be balanced and also must correspond with the positioning of the stationary contact of the rotary switch, as will be later noted. Thus in potentiometer leg i2 comprising xed resistor 36 and potentiometer 31, the iixed resistance is twice as large as the variable resistance, and the variable resistance 31 is connected directly to common conductor 35. The sector of the balancing variable impedance winding Bl which corresponds with this leg l2 is the 60 sector from the tapped connection to common conductor 35 extending clockwise in the direction of the rotation of the wiper 82. The voltage drop across the iixed resistance of the potentiometer leg I2 and across the remaining portion of the balancing impedance winding 8| will be approximately edual and, depending upon the position of the wiper of potentiometer 31, a point of eoual voltage to that contacted by said wiper will be contacted by wiper 82 of the balancing Variable impedance 20 as the wiper 82 rotates through this 60 sector. Such a condition is also true of the corresponding 60 portion-of the balancing vars labile-impedance winding 8| positioned counterclockwise from common conductor 35, but because ofthe positioning of the stationary switch contact which corresponds with the potentiometer leg I 2,` the output circui" ior potentiometer leg l2 and balancing variable impedance 2D will be made only when this particular switch circuit is` made, as will' be later described.

In a similar manner, the fixed resistors il and [l2 are each equal in ohmic value to the variableresistor M. ofv potentiometer leg I3. Variable resistor or potentiometer 4l is placed in series between the two fixed resistors 4i) and d2 so that the center portion of potentiometer leg i3 is variable. The corresponding portion of the balancing variable impedance 2t within which potentiometer leg i3 can be balanced is that 50 sector located half way between common conductors 34 and 35. Since the movable contact or wiper of potentiometer 4l is connected to the stationary switch contact 65 which corresponds to this position for clockwise rotation, the second sector of winding 8| located clockwise from the tanned connection of conductor 35 is the portion within which this potentiometer leg i3 will be balanced.

The potentiometer leg I4, which is similar in structure to leg l2, contains a fixed resistance All which is twice the ohmic value of the variable resistance t3. Variable resistance or potentiometer is is located along the extremity of potentiometer leg i4 and connected directly to cornnion conductor te. In the manner described above, the corresponding portion of the balancing variable impedance winding 8! which corresponds or contains points oi equal potential with that of the variable resistance or poteL tioineter dit is the 66 sector nearest the common conductor 34. The wiping contact of potentiometer 63 is connected to the stationary contact Si' ot rotary switch 63 which contact is located so that it is contacted. and swept through du. g the time that wiper S2 is passing through this third 60 sector of impedance winding 3l,

In a similar manner the potentiometer legs l5, i6 and il, comprise iixed resistors and variable resistors or potentiometers of such values and with potentiometers placed within the extremities of potentiometer legs in such position that each leg can be balanced within a deiinite 60 sector of the balancing variable n cxdance winding 3l. Potentiometer leg i5 is id. al in construction to potentiometer leg le. .ln the same manner, potentiometer legs l 53 potentiometer legs il and i2 are similar in construction. The wiping contacts of the potentiometers in each of the respective legs are connected to stationary switch contacts which correspond in position to the respective sectors or the balancing variable impedance winding 8i within which each of these potentiometer legs contact 64 of switch 63 and the amplifier 2l, and

the ground connection between amplifier 2| and the wiping contact 82 of the balancing variable impedance- 20. Effectively, each of the potentiometer legsi2ll form a Wheatstone bridge circuit with the balancing variable impedance, and the circuits between the wipers of the potentiometers of each legA and the balancing variable impedance 2i). comprise the output diagonal of' each bridge. Potentiometer 31 of potentiometer leg or branch l2 of the network ill is connected from its wiping contact by means of conductor i3 to the stationary contact 65 of rotary switch (i3. The rotary contact 64 of switch 53 is connected by means of conductor 99 through an input resistor oi amplifier 2l to be further described, to a ground connection. Grounded ccnductor lit of thewiper 82 of the balancing variable impedance 2E) completes this output circuit. Similar connections by means of conductors lil-'ll and 8G exist between the potentiometer-s 4l, 43', 45. .'iii and 53 of potentiometer legs or branches l3-ll, respectively, and the stationary switch contacts (i5- 6.1 and lil-'E2 of the rotary switch 63. The connection from the rotary contact 6ft of` switch 63 through the axnpler to wiper e2' of the balancing variable impedance 2d is common to all output circuits.

Motor which drives the wiper 52 of balancing variable impedance '2S and the rotating contact 55 of rotary switch 63 by means of shaft 8d is continuously operated at a uniform speed being energized from the main source I i through two conductors |93, itil. Control switch schematically shown in conductor 93, provides a means of stopping and starting said motor. The motor 85 also provides motivating power tor operating recorder 24, as will be further described as the disclosure proceeds.

The rotating elements of the balancing variable irnnedance 2E! and the rotating switch B3, in the present arrangement, are mounted on shaft 84 in the same angular position and rotate in a clockwise direction at the saine speed, each cornpleting one revolution and returning to the starting point in the saine period of time. In this manner, output circuits are provided from all of the potentiometers of the branches or potentiorneter legs lE-il to the balancing variable impedance 2i) (in sequence). The size or length of each stationary contact of switch 63 is such that it approaches a 60 sector. Similar to a 50 sector of the balancing variable impedance winding t! and hence the output circuit is established and maintained during the period in which the wiper Sii of balancing variable inipedance 2G sweeps through the 50 sector o winding 8i within which the respective potentiometer legs can be balanced.

Referring to Figure 1, and assuming the positions of the respective rotating elements as shown, it is seen that potentiometer leg l2 is being balanced by balancing variable impedance 3. As the rotating contact @4 of switch E3 makes contact with the stationary contact E5, the output circuit between potentiometer 3l and balancing variable impedance 2li is established, as follows: contact or" potentiometer conductor i3, stationary contact 65, rotating contact E i, conductor input resistor Si of amplifier 2 i, ground connection B3 of ainpliiier grounded conductor 33 of balancing Variable impedance 2Q, to wiper S2 of impedance 2Q. At the saine time, wiper 82 will start rotating through the 60O sector of winding 8l which contains points of equal potential to that existing in potentiometer 3'|. Assuming that the wiper of potentiometer 3`| is positioned somewhere near the center of its resistor element, an immediate potential appears across the output circuit. IThis potential or voltage across the output circuit decreases to zero as wiper 82 reaches a point of equal potential with that of the wiper of potentiometer 3l and increases to a maximum again with an opposite phase relationship or direction of polarity as wiper 82 sweeps past that balance point. When the rotating contact 34 reaches a point where the next stationary contact 66 is being contacted, the output circuit of potentiometer leg I3 is established. At this time, Wiper 82 of balancing impedance 23 is sweeping through the second 60 sector ofl the impedance winding 8| which corresponds with the potentiometer leg |3. The same operation occurs continuously as the rotating contact Eli of switch 63 and wiper B2 of balancing variable impedance 2t rotate in synchronism. As conditions which operate the sensing elements 55-5'|, 63-32 vary, the balance points of each of the respective potentiometer legs or branches |2|l vary along the periphery of the impedance winding 8| but remain Within their respective sectors. The eifect on the output circuits of these potentials which vary in magnitude and shift in phase as they are sequentially applied to the amplifier and relay unit will become evident as the disclosure proceeds.

Amplifier and relay unit The amplifier and relay unit comprises a conventional amplifier 2| with two stages of amplication 8S, |36 and a pair of discriminator tubes |22, |23 which control the energization of a pair of relays 22 from a control transformer |43. The relays 22 control the energization of an inductive device or sparking transformer |73 from a D. C. battery source 23. The output from such transformer provides a surge in potential to mark the record which is being driven by the recording unit 2li.

The rst stage of amplication or amplifier tube 86 is controlled by the voltage impressed on the input resistor 8l', said grid biasing resistor being located in the output circuits of the network I3 as described above. Conductor 93 connecting the rotary switch 33 to the grid biasing resistor 8l extends to grid 9| of tube 83 to complete the biasing circuit. Cathode 92 of tube 86 is biased by an unby-passed resistor 93 which is grounded by conductor 34. Plate or anode 95 or tube 83 is connected through conductor 93 and output resistor 9i to a D. C. source 532. Conductor 96 also connects anode S5 to coupling condenser |32 which couples said anode or plate to the grid input resistor of tube |96. Grid input resistor is connected to grid |31 of tube |33 by conductor i3 which also serves to connect said grid to the coupling condenser |365 and is grounded through grounded conductor ||2. Cathode |i of amplifier tube |33 is biased by the by-passed biasing resistor Il? which is grounded by conductor |23. Condenser i3, connected in parallel with biasing resistor serves as the by-pass. Anode H3 of amplifier tube |33 is similarly connected to the D. C. source |32 through an output resistor |55 which is connected to said anode by a vconductor Illi. D. C. source |2 is in turn iiltered by a condenser li which is grounded by a conductor |0|. Coupling condenser |2 connected to anode ||3 by conductor H4, couples said anode or plate with grids |26,

|21 of discriminator tubes |22|23. Grids |23, |21 are connected to grid input resistor |33 by conductor i25, input resistor |33 being grounded to ground conductor |28. Cathodes 13| and |32 of discriminator tubes |22| 23 are biased by bypassed resistor |34 which is connected to said cathodes by conductor |33. Cathode biasing resistor |33 is by-passed by by-pass condenser |35, connected in parallel with it, and is grounded by conductor |33. Anodes or plates |31, Hill of discriminator tubes |22|23 respectively are connected to the opposite ends of secondary windings l-li of a transformer i3 so that said anodes do not have the same polarity impressed on them at the same time and hence are not conductive at the same time. Transformer |63 which serves to supply power to operate a pair of relays 22, includes primary winding |313 energized from the main alternating source through conductors 25, 26 (not shown as connected in the drawing) and the before mentioned secondary windings |35, |43. IThe opposite end of each secondary winding |45, |43 which is not connected to the plates of the discriminator tubes |22, |23, are connected by means of conductors ll, |52 to the energizing coils of the relay coils |31, |53 of the pair of relays 22. These relays operate independently although their operating contacts are connected in series connection and the ends of the coils, not connected to said transformer secondaries E35, |23, are connected by means of common conductor |53 to the ground conductor |54. Connected in parallel with relay coils |37, are condensers |55, l5?, respectively. One end of each condenser is connected directly to its associated relay coil. The opposite ends are connected to the relay coils through ground conductcrs |53, |33 respectively and ground conductor |53. Condensers |55, I5? serve to provide a time delay action in the decay in potential applied to one or the other of relay coils lli, |53 when its respective secondary energizing winding of control transformer |33 is deenergized by an opening of a circuit, to be later described, by one or the other of the disoriminator tubes |22, |23.

The pair of relays 22, when the operating contacts of each are closed, control the energization of the primary winding of sparking transformer Il@ from the D. C'. or battery source 23. The negative terminal of battery 23 is grounded by conductor V54 and the positive terminal is connected to one end of the primary winding lil. Primary Winding is connected at its opposite extremity by means cf conductor |66 to the movable contactV |63 of the relay actuated by coil |33. Stationary contact |6| of this relay, which cooperates with the movable contact |63 is connected to the stationary contact |52 of the relay Whose coil |53 operates its respective movable contact |34. Movable contact |34 is connected to ground conductor |65 to complete the energizing circuit of the transformer primary winding through the relay contacts to ground. Condenser |31, connected between conductor |66 and ground conductor |13, serves to provide a means of arresting arcing across the contacts of relays 22 which might occur after current ow through the primary winding has been established by the making of the contacts of both relays 22 and the circuit is again reopened. An inductive surge occurs in the primary of transformer llc when said primary is energized from the battery 23 as follows: positive terminal of battery 23, primary winding Ill, conductor |66, relay conkthe grid biasing resistor of tube |35.

9 tacts |63, ISI and |62, |64, and ground conductor |65 to ground conductor |14 of battery 23. This surge impresses momentarily a high potential upon secondary |12 of transformer |13 to energize a circuit for the recording apparatus 24. which will be later described.

Current iicw in the output circuits of the network Ill and through the input resistor 81 of the first stage of amplication of amplier 2| causes a voltage drop to occur across said resistor which is applied to grid 9| by reason of the following circuit: from cathode 92, through ground conductor 54 and ground conductor 38, and resistor 81 to grid 9|. The amplified A. C. component cf the voltage impressed on grid 3| will be impressed on resistor 91 and establish a voltage drop across Tube |56 is similar to tube 85 and functions in the same manner. The A. C. component of the output of tube |56 is impressed across grid input resistor |33 of discriminator tubes |22, |23 to impress on the grids |25, |21 the same potential at the same time. The anodes |31, |45 of discriminator tubes |22, |23, respectively, have applied thereto voltages opposite in phase since they are connected to extremities of the secondary windings |45, |48 of control transformer |43 which are opposite in phase and the cathodes are connected together. One or the other of said discriminator tubes |22, |23 will be conductive depending upon the phase relation between the bridge output and the voltage energizing the transformer |43. Thus as the phase of the input voltage tothe grid biasing resistor 31 of tube 85 reverses, the .phase of the output of network lil reverses-that is at the time when the balance point for one of its branches is reachedone of the discriminator tubes will stop conducting and the other will start conducting. Relay coils |41, |56 which are controlled by said discriminator tubes |22, |23 are independently energized through transformer secondaries |45, |45 by circuits which prevent energization of the said relay coils at the same time. Coil |41 is energized through a circuit as follows: secondary winding |45 of transformer |43, conductor I3I, anode |31 of tube |22, cathode I3I, conductor |33, resistor |34 and by-pass condenser |35, ground conductor |36, ground conductor |54, conductor |53, coil |41, conductor I| to secondary winding |45. Coil |50 is similarly energized through a circuit as follows: secondary winding |43Yof transformer |43, conductor |42,

anode of discriminator tube |23, cathode |32, conductor |33, resistor |34 and by-pass condenser |35, ground conductor |35, ground conductor |54, conductor |53, coil |55, conductor |52 to secondary Winding |45. Since each of the time delay condensers |55, |51 has one plate grounded to ground conductors |55, |58 respectively, a parallei circuit is established around each relay coil |41, respectively, and a time delay in the drop out of each relay occurs when its energizing main circuit is broken. Thus when the energizing circuit for one relay coil is broken and circuit for the other coil is made, the rst named coil will remain energized momentarily because the charge built up on its respective condenser which is connected in parallel With the relay coil will be impressed upon said coil While the condenser discharges through it. During this interval, both relay coils Will be energized and their contacts closed, thereby providing a circuit for energizing the sparking transformer |15, as described above. The momentary current flow from the D. 1C.

source 23 through the primary Winding I1| of sparking transformer |10 builds up a voltage in the secondary Winding |12 which is sumciently large to record on the recording unit 24.

Recording unit Recording unit 24 is comprised of styli apparatus |813 and chart drive assembly 13|, both of which are positioned by the driving motor 85. Chart drive assembly ISI includes a driving roller |52, free roller I recording sheet |88, geared Ashaft |84 `attached to the driving roller |82, a

second geared shaft |85 directly attached to motor 35 and belt drive pulleys |85. Styli apparatus |35 includes belt |92, styli |9| attached to belt |52, ground plate |81, grounded conductor I brush and holder |83, conductor |11, and resister |15.

VMotor 85 drives the driving roller |82 through a geared connection between geared shaft |84 and geared shaft |85, said first named shaft being fixed to the driving roller. The chart record |88, or the unmarked portion of which is stored on free roller |83 Vis fed from the free roller |33 through an opening or space `between belt |32 and the ground plate |81 to the driving roller |52 where the marked portion of said record is stored. Simultaneously the motor 85 drives one of the belt pulleys |85 which is keyed to shaft |85. Belt |32, which is made of an electrical conductive material, has the Vstyli ISI attached to it and is mounted on the belt pulleys |85. The diameter of the pulleys |35, the length of the belt |52 and the number of the styli |A9| .attached to belt I 52 are all factors which are dependent on one another. In order to record continuously all of the balanced conditions for each of the branches or legs |2|1 of network l5, a stylus ISI must cross the chart record |38 -with each revolution of the rotary switch |53 and balancing variable impedance 25. This is the time required to balance all of the network branches. It follows that the spacing of the styli |8| on belt |92 is equal to the distance of the width of the chart record |88 or the distance that the belt |92 travels within one revolution of the belt pulley |85.

In the present arrangement, as shown in Figure 1, the length of the belt |52 is equal to four times the width of the chart record |88, and the four styli |52 are spaced a distance apart equal to the Width of the chart record |88. Belt pulleys |85 are such diameter that their circumference is equal to the spacing between the styli |92, thereby insuring movement of the styli the width of the chart record |88 during each revolution of the belt pulleys |85` cr the driving motor 85. Belt |52 is also positioned on pulleys |86 so that one of the styli |9| is located at the edge of the chart I 88 ready to start movement across the width of said record as wiper arm 82 of balancing variable impedance 25 and rotary switch contact 64 of rotary switch 53 are in position to start across a given sixty degree sector of winding 8| and the stationary contact 55, respectively. This insures proper spacing of the records into channels of equal width and further facilitates identifying each of the records with its respective circuit. This use of a plurality of styli |9| on belt |92 presents an advantageous arrangement in permitting the recording, continuously, of the effects of a plurality of networks which are connected sequentially to a recording apparatus. Not only can the spacing of the records be obtained, but the marking apparatus or ystyli is always in position to record on the record sheet and no loss of time or skipping of operations of the networks occurs. Such an arrangement presents a definite advantage over the common type of recording apparatus where either the marking apparatus or the record sheet has to be repositioned before a new sequence of operation can take place.

Operation of Figure 1 The operation of the subject recording apparatus can best be described by assuming the positions of the movable elements as shown in Figure l. Rotary contact 54 of switch 63 is starting to make contact with the stationary contact 65. Wiper 82 of balancing variable impedance 2|] is starting to sweep through the 60 sector of winding 8l after passing the tap to conductor 35. One of the styli |9| is just starting across the record |88. Wiping contact of potentiometer 31 positioned in potentiometer leg or branch l2 to which the stationary contact 65 is connected, is positioned by sensing element 55 somewhere along the resistor of said potentiometer. While all of the potentiometer legs |2| 1 of the network ||J as well as the balancing variable impedance 2|] are energized from source Il, the slider of only potentiometer leg |2 is connected to the balancing impedance 22|. Effectively a Wheatstone bridge circuit is obtained between potentiometer leg |2 and balancing variable impedance 2|! whose input is supplied by conductors 32, 33 from transformer secondary 3| and whose output circuit, as described above, is established with the making of contact between rotary contact 6d and stationary contact B5 of switch 63.

Motor 85, continuously energized from source il, drives simultaneously the rotary elements of the balancing variable impedance and the rotary switch, the driving chart roller |82 and the styli apparatus. Immediately upon establishment of the output circuit for potentiometer leg l2, a voltage or signal will be imp-ressed upon the amplifier through input resistor 81 since the wiper 82 is in Contact with a point on impedance winding 8| whose potential differs from the potential existing at the contact point of the Wiper of potentiometer 31. Depending upon the sense or phase of this signal, one or the other of the discriminator tubes |22, |23 will become conductive and establish an energizing circuit for its respective relay coil. Since only one relay is energized, the energizing circuit of the sparking transformer |10 is not completed and no output from said transformer occurs to mark the record. As the rotating elements, wiper 82 and contact 64 and belt |92, continue to move, a point on the impedance winding 8| is contacted which is of the same potential as that of the contact of potentiometer 31 and a balance condition occurs at which time no current or signal flows in the output circuit. The output of amplifier 2| is then momentarily cut off but since time y'This change in phase causes the discriminator 12 tube, heretofore inoperative, to become Vconcluetive and permit the energization of the relay. Momentarily while the first named time delay condenser discharges, both relay coils |41, |50 are energized and their contacts make to estab- VliSh an energizing circuit for sparking transformer |10. As soon as the condenser discharges, its respective relay coil becomes deenergized and its operating contacts open breaking this energizing circuit. The output of the secondary winding |12 of transformer |10 is impressed upon the styli apparatus |813 in the following circuit: transformer secondary |12, resistor |15, conductor |11, brush and holder |89, belt |92, styli |9|, ground plate |81, ground conductor |90, to grounded tap |15 of transformer secondary |12. The high potential obtained from transformer |10 bridges the gap between one of the styli |9| which is then passing above the ground plate |81, and the ground plate |81 burning a record mark of the balance point on the record |88. The network unit, as disclosed above, is not, however, limited in its use to recording apparatus. Such a unit could be readily adapted to perform any desired controlling function by simply using its output to control through itself or any other intermediate devices.

After the balance point is passed and until the next stationary contact segment is reached, no further change takes place in the amplifier and relay unit. The spacing between the stationary relay contacts 65-61 and 'Hl-12 provides sufcient time interval between the change from one output circuit to another to prohibit both relays from being made again as the phase of the output changes. As the rotary elements sweep across the next stationary contact 56 and its similarly positioned portion of the winding 8| corresponding to potentiometer leg I3, the same operation occurs. The records for each network branch or leg |2| 1 are thus kept within a definite channel or spacing on the chart record |88 as governed by the distance that a stylus moves while the rotary contact is in contact with the stationary elements of the rotary switch. In the present apparatus six such channels will occur. Variations in conditions which operate the sensing elements 55-51 and Bil-62 shift the positions of the respective wipers on each of the potentiometers and hence the balance point for each network branch or leg, but the records indicating this shift are contained within the limits of the above named channels.

It'is evident from the foregoing description that the amplifier does not permit energization of the sparking transformer at the instant the balance condition for each bridge of the network occurs. Not until after this balance condition is passed and an unbalanced condition occurs are the styli energized by a potential from the sparking transformer to mark the chart record. This time interval which occurs between the balance condition of the bridge and the marking of the chart record is constant because the energizing voltage and the speed of the rotating parts are constant. Thus while the individual record mark 1s not made at the time the bridge is balanced and hence not at the time when the wiper 82 of the balancing potentiometer is positioned on a point of the winding 3| which corresponds to the instantaneous value of the condition, the same amount of offset occurs on the chart record for each recording and the variation in values which occur are truly represented. In this respect, the relay and inductive device is operated as an incident to each network being balanced. In calibrating the recording unit, a zero or normal value correction can be made b-y shifting the datum line on the recording chart when a calibrated chart record is used. This will make the recording mark correspond with the value of the condition present during the balancing of its respective bridge network. Since such calibration of recording devices is common practice this operation was not included in the disclosure.

Figue 2 The modification of the recording apparatus, as shown in Figure 2, discloses another embodiment of the network unit which operates through the amplifier 2| and relay unit 22 to record continuous variations of a plurality of conditions on the recording unit 24. For simplicity in disclosure and discussion, only the network is shown but it is understood that it will be used with the amplier, relay and recording units of Figure l.

The network unit as shown in Figure 2, comprises a plurality of bridges 2II-2|5 the output circuits of which are connected sequentially in series with the output circuit of a balancing bridge |99 and the effect of said combined circuits is impressed upon the amplier 2| and relay units 22 in the same manner as disclosed in Figure 1. The output of each of the bridges 2| I-Zi is individually balanced by the output of the balancing bridge |99 connected in series with it so that the signal to the ampliiier is null when the balancing bridge has an output which is equal to and opposite in sense to the output of said bridge. As such a condition is occurring in the manner described above, the ampliner and relay unit operate to control the energization of an inductive device Ill? and the potential thus obtained marks the record ISS of recording unit 22 to record such balance points.

Bridges 2| |-2|6 comprise centering potentiometers 23I-235, ratio potentiometers 21H-255, energizing transformers 25|-255, sensing potentiometers 22l-22, and sensing elements 55-57 and EEB-52. In bridge 2| I, centering potentiometer 25|, whose manually adjusted wiper is connected to balancing bridge I 99 in a manner to be further described, is connected in parallel with sensing potentiometer 22l by conductors 2 l i and 222' to form said bridge. Bridge 25| is energized by transformer 25| whose primary windingl is energized from the common source ii (not shown) and whose secondary 25| is connected to the opposite terminals of the resistor of ratio potentiometer 22|. One extremity of ratio potentiometer 24| is attached to one side of said bridge at conductor 2I'I and its wiping contact is connected to the opposite side of the bridge at conductor 229. Sensing element 55, shown in Figure 2 'as a coiled bimetallic strip, actuates the contact of sensing potentiometer 223 and is insulated from it. The contact of potentiometer 22| which is actuated by sensing element 55 is connected to the stationary element or contact 22| of switch 280 by conductor 29I for purposes which will become evident as the disclosure proceeds. Bridges 2|2-2l5 are similar in construction and function to bridge 2H, described above, in the following manner. Bridge 2I2 comprises centering potentiometer 252 and sensing potentiometer 222 connected in parallel by conductors 221 and 229. Energizing transformer 252 comprises primary winding 2l|2 energized from source I I and secondary winding 262 connected to the opposite terminals of the resistor of ratio potentiometer 242. The output terminals of ratio potentiometer 242 are connected in parallel with the above named potentiometers, one extremity being connected to .conductor 221 and the contact of said potentiometer being connected to conductor 235. Bridge 2l3 comprises centering potentiometer 233 and sensing potentiometer 223 connected in parallel by conductors 231 and 249. Energizing transformer 253 of bridge 2 I3 comprises primary winding 273 energized from common source I I and secondary winding 253 connected to the opposite terminals of the resistor of ratio potentiometer 223. The output terminals of ratio potentiometers 223 are connected in parallel with the above named potentiometers, one extremity being connected to conductor 221 and the contact of said potentiometers connected to conductor 235. Bridge 2id comprises centering potentiometer 234 and sensing potentiometer 224 connected in parallel by conductors 251 and 255. Energizing transformer 254 of bridge 2 l comprises primary winding 2'54 energized from common source Il and secondary winding 25.4 connected to the opposite terminals of the resistor of ratio potentiometer 24d. The output terminals of ratio potentiometer 2M are connected in parallel with the above named potentiometers, one extremity being connected to conductor 25'! and the contact of said ratio potentiometer being connected to conductor 259. Energizing transformers 25 i-254 of bridges 2| |-2 I 4 have a secondary output potential which is equal to that of transformer 255 of balancing bridge |99. Due to the positioning of the wiping contact ratio potentiometers 22d-21M of said bridges, their energizing potential is equal to approximately one-half of the energizing voltage of balancing bridge I 99.

Bridge 2I5 comprises centering potentiometer 235 and sensing potentiometer 225 connected in parallel by conductors 257 and 25E). Energizing transformer 255 of bridge 2 I5 comprises primary winding 2'5 energized from common source and secondary winding 255 connected to the opposite terminals of the resistor of ratio potentiometer 245. The output terminals of ratio potentiometer 245 are connected in parallel with the above named potentiometers, one extremity being connected to conductor 251 and the wiping contact of said ratio potentiometer being connected to conductor 269. Bridge 2|5 comprises centering potentiometer 236 and sensing potentiometer 225 connected in parallel by conductors 257 and 258. Energizing transformer 256 of bridge 2|5 comprises primary winding 215 energized from common source |I and secondary winding 25B connected to the opposite terminals of the resistor of ratio potentiometer 246. The output terminals of ratio potentiometer 2Li5 are connected in parallel with the above named potentiometers, one extremity being connected to conductor 257 and the wiping contact of said ratio potentiometer being connected to conductor 21D. Energizing transformers 255, 255 have a secondary output of twice the voltage of transformer 252 of balancing bridge |99 and transformers 25h- 254 of bridges 2|l-2I4. Due to the positioning of the wiping contacts of the respective ratio potentiometers 24E-246, the energizing voltages of said bridges are equal to the energizing voltage of rebalancing bridge |99. The sensing elements 56-51, (5U-62 are similar in construction and function to sensing element 55 each being respectively connected to and insulated from the wiping contacts of sensing potentiometers 222-226. The contacts of said sensing potentiometers are connected to the stationary elements 282-282 of switch 280 in the following order. Contact of potentiometer 222 is connected by means of conductor 292 to stationary switch element 284. Contact of sensing potentiometer 223 is connected by means of conductor 293 to stationary switch contact 283. Contact of sensing potentiometer 224 is connected by means of conductor 294 to stationary switch element 282. Contact of sensing potentiometer 225 is connected by means of conductor 295 to stationary switch element 285. Contact of sensing potentiometer` 225 is connected by means of conductor 296 to stationary switch element 286.

The stationary elements 28E-286 of rotary switch 282 which were recited above form an annular shaped stationary contact structure whose individual contacts or elements are separated from one another by pieces of insulating material. Pivoted from the center of said ring is a rotary wiping contact 64 which is driven by shaft 3M through gear train 29?. The gear train 297 is driven from the shaft Bil of motor 85, the gear reduction being two to one. Wiping portion of contact 64 is insulated through the main portion of the contact arm and hence is insulated from the driving shaft and gear train. Conductor S1) connects the rotary contact arm 64 with amplier 21 through grid input resistor 8'1 in a manner previously described.

The output circuits for the bridges 21 1-216 extend from the wiping contacts of their respective sensing potentiometers to the stationary elements of the switch 28, to the wiping contact of said switch and through conductor 9U to the grid input resistor 8l of amplifier 21. The other extremity of the circuits extends from the wiping contact of the respective centering potentiometers of bridges 2li- 21B to the tapped connection of the secondary winding 202 of transformer 220 which forms a part of the balancing bridge 1.99. These connections with the above named transformer taps are effective to connect the output circuits of the respective bridges with the output circuit of the balancing bridge to complete the circuit through the amplier 21 in a manner which will become evident as the disclosure proceeds.

Balancing bridge EQ2 comprises the balancing variable impedance 29 and energizing transformer 22! connected in series by conductors 1915 and le?. Balancing variable impedance 2S includes annular resistor winding 31 which is connected to conductors idd, 13? by two taps spaced 180 apart, and wiping contact 82 driven by and insulated from shaft 861 of motor 85 (not shown). Wiper S2 is grounded by conductor 83 to complete the output circuit to ampiier 21, that is, the circuit through grounded conductor 83 to grounded conductor 33 of biasing resistor 87 in the rst stage of ampliiication of amplier 21. The primary winding 2N of energizing transformer 2iEl is energized from common source 11 by connections not shown in the drawing. Secondary winding 22 of transformer 28@ which is connected at its extremities to conductors 19t, 191 includes tapped connections 253, 262 and 2l5, the purposes of which will become apparent as the disclosure proceeds. Bridges 21E-216 are connected in series with balancing bridge 199 at the above named tapped connections in the following manner. VThe wiping contacts of centering potentiometers 231 and 232 of bridges 21 1 and 212 respectively are connected by common conductor 206 to tap 203. The wiping contacts of centering potentiometers 233 and 235i of bridges 213 and 21d, respectively, are connected by common conductor 2li? to tap 255. The contacts of centering potentiometers 235 and 236 of bridges 215 and Elfi, respectively, are connected through common conductor 2M to tapped connection 204. Secondary winding 252 of transformer 259 in bridge 1% is so constructed with direrent taps 223-225 that the positions of the impedance wiper 82 of balancing variable impedance 2t for the balance point of said bridge are located at different points about the impedance winding S1 for each tap. Thus, considering a connection to the balancing bridge 199 at tap 223, it will be noted that under the balance conditions for the balancing bridge only, the wiper 82 will be located at winding B1 at a point onequarter of the distance along said winding from tapped connection of conductor 196. Similarly the position of wiper 32 when the balancing bridge 199 for taps 294 and 265 will be located on the winding 81 at points one-half the length of winding 31 between conductor taps 556-191 and three-quarters of the length of winding 81 from the conductor tap 19B respectively. Similar points would be found on the other half of impedance winding 81.

The input voltage to all transformers in the network are the same since all are energized from the connnon source l1 (not shown in Figure 2). The secondary windings 262 and 261-254 have the same potential output. Bridges 211-214, however, which are supplied by transformers 251-255, have just one-half of the potential applied to them as compared with bridge HB9 since the secondary windings 261-264 of said transformers are connected to the ratio potentiometers 21H-24S which act as voltage dividers, their respective wipers being approximately centered. Transformers 25E-25E, while having the same applied potential to their respective primary windings 2'i5-2'i, have an increased output from the secondary windings Z55-266 which is twice as large as the secondary output of the before mentioned transformers. These secondary windings, however, energize ratio potentiometers 2435- 2i5 which act as voltage dividers in energizing the bridges 215--2i6 and due to the positioning of the wiping contacts of said ratio potentiometers, the voltages applied to these bridges are approximately one-half of ie transformer outputs or a voltage which is equal to the energizing voltage of the balancing bridge 19S. While the position of the wiping contacts of potentiometers ZIM-225 is generally set at a point midway between the extremities of its respective potentiometer winding, as noted above, said contacts are manually adjustable to decrease or increase the voltage applied to their respective bridges. A change in this applied voltage changes the unbalance voltage or the bridge for a given movement of thesensing element and requires increased or decreased movement of the balancing variable impedance wiper 82 to balance the new unbalanced voltage for the same condition. This effectively expands or contracts the scale of the recording instrument with respect to the value of the condition being reported.

For practical purposes, the wipers of the centering potentiometers 23l-23 of bridges 211-215 are xed at the centers of their respective potentiometer windings so that the maximum of unbalance voltage which can be obtained from these bridges is equal to one-half of its applied or energizingirvoltage. The centering potentiomfeter provides a` means 'of :manually.adjustingA the f. relation between: centeringfpotentiometerz' and` sensing potentiometer fornormal position of" theV sensing elements 552--51 and 69--62' so Y.that the output oi said bridge will. be aero under :.th'ei.

normal conditions andthevbalance pointof vthe combination o1" bridge'and balancing .bridgewill I occur lat the balance point of the balancing bridge.

Bridges 2li- 2M whose., applied. potential is? on'eehalf the potential appliedto balancing bridge I 92 .and whose. maximumV unbalance is one-half.

of that applied potential Yorone-'fourth ofthe ape plied potential to balancing bridge |99, as noted' aboveyare connected'tothe balancing bridge 1| 99 by circuits previously Vrecited to Ataps 293 'and Y205.-

These taps are at points on thetransformer'secgondary winding292'which possess a' .potential .of one-quarterdthe applied. potential. of .the balance ingv bridge.

and.. |91. bridges connected in series with. thebalancing bridgeedual. to one-quarterof the totalJapplied* voltageto` thebalancing bridge |99, th'ebalancing?, variable impedance .2o can balance/.such signal or unbalance Vfromxthe bridges 'by' movement over one-'fourth of. the distancealongithe winding 8| l between the conductor .taps |96J.and.| 91 in either direction .from said balance vpoint which corre. sponds tsthe .respective taps..

A relativearnovement betweenthe wiper.82:.of balancing impedanceZIJ-.and the' rotary switch contact .54 of rotaryswitch 280 as lpreviously noted. was in the'ratio of'two to one oritworevolutions 1 of wiper 82 to asingle revolution ofthecontact 54; Assuming thepositions of vthese respective.. elements as shown in Figure 2; the/rotary switch..

contact'd will establish contact with thestationary, contacts 28|-284'and complete the output circuits for thenetwork with bridges .21| |-2'I 4 in..

a sequence-noted below vasithe wiper 82 of ibalancing-impedance20 moves throughmoria single revolution. During the .period Whenithe .sWi-tch:

contact 64 is in contact with one of thesefstationaryelementathe wiperi82 will move through a\90 sector along the impedance. winding' 8|..

Since the balancepoint ofbalancing bridgezis loi cated midway alongfthis sector vof 'mov-ement off. the wiper 82, there `issuicient rangefonxeither` side of thenormal balance .point to -rebalance the i maximum unbalance of the -bridgeiconnected in series withvthe 'balancingbridge"atgthat period. f

In this manner; somewhere Within the rst90 sector of balancingimpedance winding 8 wiper 82wi1lreach a point where theoutput of the bal.-

to the amplier 2|.

element 282,'. wiper -82 will be sweeping through the second 90? sector of windingrl and the same operation will occur. As the rotating Contact. makes contact withy the stationary-.element -283,

bridge 2|3 will be connected in vseries with the-y balancing bridge.|99 and` the combined output of the two bridgeswill be-impressed upon the amplier 2| as wiper 82-sweeps at the third 90 sector of impedance winding 8|. tion occurs when. the rotary contact .64 makes contact.. with the stationaryv element.28l and The .balance points on 3 impedance windingrl which .correspond .to saidtapsarelocated. at pointsv along the Iwinrlirnggl .abone-v fourth of the distance between conductors |9|v With the maximum imbalance; of.k

The same voperabridge 2 2 is yconnected in series with balancingv bridge |99. It is to be notedthat thesequence' invwhich v.the bridges 2| l-ZM .are connected to the balancingbridge is dependent'on the connecf tion of the individual bridgeto the transformer` tapsi203-2D5 :of the balancingbridge |99 since' the wiper 82 of the balancing variable impedance 20 must be operating on the section of winding 8 which fcorresponds .with r thel tap connection with kwhich saidA bridge is connected.`

Bridge I2|5and`bridge ZIE-@will be connected setpientiallyy in series with the balancingY bridge |99=withfthe secon'drevclution'of wiper '82 of balancingliinpedance V29and -the'second halffof revolution l.of rotary., switch contact 64 of switch 280. Since the-balance point'of balancing bridge |99 correspondingito tap.204.0f secondary Windingr-2 921s locatedmidwaybetween the conductor` tapszlil,v |91 on impedance winding 8| and since the maximum. unbalancevoltage ofthe bridges 2 |5 .and 2 6 is approximately one-half of the volt-- age. applied to said bridges and `the balancing bridge 99,-it follows that the positioning of wiper 32, ,90'on away from the mid-pointof the Winding.k

8| .betweenconductor taps |96, |91 will balance a maximum imbalance condition. Movement of the wiper 82 on the lwinding 8| from the tap of conductor., |96 yto thetap of conductor |9'|`bal ances bridge 2|5 during the period whenV rotary Contact 54 is contacting stationary element 285 ofswitch 289. During the second half revolution ctw-iper 82, they same operation occursduring.

whichlthebridge 2| is balanced.

The operation `of the recording unit24, amplier 2| and relay 22 unitwith the present network .is the same as that described for the network embodiment-.lof Figure l. The styli apparatus |30 (not shown) moves at the same speed as shaft l8'4 Vandhence the belt pulleys |86 complete tworevolutions during the period'in which, all bridges 2l |-2i6'are balanced. During the rst revolution when one stylus moves acrossthe record sheet |88, bridges 2||-2|4 are balanced by balancing bridge |99 and these balance points are recorded within four channels corresponding to the sectors of theimpedance winding 8| within which ther network is balanced or'during the vperiods in which the output circuit for each' of the bridge combinationsv are made through the rotary switch. During/the secondrevolution of the wiper 82 on winding 8| of 'balancing impedance 29,-when the next stylus moves acrossthe recordl sheetv|89, bridges 2|l= 2| 6v` are-balancedby'balancing bridge |99 and' the record'of their balance lpoints are superimposed on ythe'records of the rst named bridges each being limited within a-channel correspond-Y ing to the periodsv during` whichy their respective-output circuits are completed of the balancingibridge |99to. the amplier 2| or limited to one-half of the chart record.

Amplifier 2|, as previously described, has the same rtypeA of varying voltage or signal applied to it-from the present network as each output lcircuit'is. established, and the relays 22.1010 not operatethe inductive device to record the bal anceepoint until thisioutput or signal decreases to zero and.l thenv appears again. inr an opposite senseindicating that a ybalance condition has just been passedv as described above. The recording.:

unit. then. operates asheretofore described.

Numerous objects and advantages of my in.y vention have` been set :forthV in thel foregoingY description, togetherwith details of the structurel and function ofthe invention, and the novelv features thereof are pointed out in the appended claims. The disclosure, however, is illustrative only and I may make changes in detail within the principles of the invention, to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.

I claim:

1. Electrical apparatus for recording a plurality of variable conditions, comprising' in combination, a plurality of variable voltage means each of which is variable within predetermined limits in response to variable conditions the limits of one being non-overlapping in respect to each other, a uniformly variable voltage producing means variable over range which includes the summation of the individual limits of said iirst named voltage producing means, continuously operated motor means, switching means driven by said motor means, amplifier means including discriminator means, means including said switching means for sequentially connecting said last named voltage producing means through said amplifier means to each of said first named voltage producing means to provide a plurality of balanceable networks the output circuits of which include said amplier means, said output circuits of each of said networks having impressed thereon an unbalanced voltage which varies in phase and magnitude, relay means including a pair of relays each having associated time delay means, inductive means, recording means, one of said relays of said relay means being operative when a voltage of a given phase occurs in said output circuits of said networks, the other of said relays being operative when a voltage of an opposite phase occurs in said output circuits of said networks, and means including said time delay means energizing both of said relays as said voltage in the output circuit of said network changes sense, said inductive means operating to record on said recording means as both of said relays are energized.

2. Electrical apparatus for recording a plurality of variable conditions, comprising in combination, a plurality of variable impedance means, means energizing each of said variable impedance means from a source of power, certain of said impedance means being variable within predetermined limits in response to variable conditions, the limits of each of said condition responsive impedance means being nonoverlapping in respect to each other, means for varying one of said impedance means at a uniform rate over a range which includes the summation of the limits of said iirst named impedance means, continuously operated motor means, switching means driven by said motor means, amplifier means including discriminator means, means including said switching means for sequentially connecting said last named imp-edance means through said ampliiier means to said rst named impedance means to provide a plurality of balanceable networks the output circuits of which include said amplifier means, said networks each being balanced within predetermined values of said impedance varying at uniform rate, relay means including a pair of relays each having associated time delay means, and energized from saidamplier means, said relay means being energized independently of one another depending upon the phase of the voltage energizing said amplifier means, inductive means,

recorder means, said inductive means being op erative upon energization of both of said relays to record on said recording means, and means including said time delay means energizing both of said relays upon change in phase of said voltage as an incident to each network passingthrough its balanced condition.

3. In a device of the class described, a plurality of voltage producing circuits each including iixed and variable electrical impedances,

each of said variable impedances being variable in response to a predetermined condition, a balancing voltage circuit including a single variable impedance, electrical connection means connecting said plurality of said voltage producing circuits and said bal-ancing circuit together such that all of the circuits have the same potential drop occurring therein, output connections connected to each of said variable impedances of said plurality of voltage producing circuits at points of differing electrical potential, switching means having a plurality o1" stationary contacts and a movable contact, said ou-tput connections being connected to said stationary contacts of said switching means, a-variable position connection connected to said impedance of said vbalancing circuit and adapted to be varied cyclically through a predetermined range of operation, amplifier means connected to said movable contact of said switching means and said variable connection of said balancing circuit to complete an electrical circuit therethrough, means operating said switching means and said variably positioned connection of said balancing circuit simultaneously to move said movable contact relative to said stationary contacts and said variably positioned connection relative to said impedance to connect said output connections to said variable connection of said balancing circuit when said variable connection is approaching a potential point substantially equal in amount to the potential existing at said respective output connection, said amplifier means beingsequentially operative as said variable connection reaches a point of potential equal to each of the potentials of said output connection.

4. In a device of the class described, a plurality of sensing circuits each including a iixed resistor and 'a potentiometer having a wiper, means connecting said sensing circuits together in a parallel arrangement and adapting said plurality of circuits to be simultaneously energized from a source of power, condition responsive means -attached to said wipers of said potentiometers for actuating the same in re sponse to a predetermined condition, a balancing circuit including a circular continuous potentiometer adapted to be continuously energized from said source of power, a rotary wiper for said circular potentiometer adapted to be driven continuously along the extent of said potentiometer, a rotary switching device including a plurality of stationary contacts and a movable contact, means connecting said wipers of said sensing -circuits to said stationary contacts of said switching means, further means connecting said eter, and" means including in said further meansresponding to a condition determined by the passing ofv said wiper on said circular potenti-l oineterv over a'position of electrica-l potential on said potentiometer' equal to the potential lexisting at the respective Wipers of the potentiometers of said sensing circuits then connecting to said balancing circuit.

5. In a device'of the class described, in cornbination, a plurality of sensing circuits cachincluding variable irnpedances having adjustable connections thereto, means connecting said sensing circuits together in a parallel relationship and adapting them to oe energized simultaneously from a source of power, condition responsive means attached to said adjustable connections Yof said variable iinpedances for actuating the saine' in response to predetermined conditions for varying said iinpedances, a balancing circuit including a circular potentiometer adapted to be continuously energized from said source oi'power, a rotary Wiper for said'circular potentiometer` adapted to be driven continuously along the extent of said potentiometer', a switching device including a plurality of stationary contacts and a movable contact, means connecting said Wipers ci' said sensing circuits to said stationary contact oi said switching means, further means connecting said movable contact or said switchinU device and said Wiper of said circular potentiometer, motor means for operating said switching device and said Wiper of said circular potentiometer to connect each of said adjustable connections of said plurality of sensing cir-cuits to said balancing circuit sequentially at varying positions along the extent of said balancing potentiometer, and means included in said further means responding to a condition determined by the passing of said wiper of said circular potentiometer or by position of electrical potential on said potentiometer equal to the potential existing at the respective adjustable connections of said variable iinpedances of said sensing circuits then connected to said balancing circuit.

5. a device of the class described, comprising, a plurality of sensing circuits each including po'tentionieters having adjustable wipers thereon, means connecting said plurality of sensing circuits tege er and adapting them to be energized simultaneously r om source of power, condition r .sponsive attached to said adjustable wipers of said potentioineters for actuating the saine in response to predetermined conditions, a balancing circuit including a circular potentiometer adapted to be continuously energized from a source oi power, e. rot ry wiper for said circuit tentiorncter adapted to be driven continuously along the extent or" said potentiometer, a switching device including e, plurality of stationary contacts and movable contact, means connecting s Wipers oi said sensing circuits to said stationary contact oi said switching means, further mcans connecting said movable contact of said switching devi-ce to said Wiper of said circular means responding to a condition determined by each oiV the Vadjuf-:table connections ci said vari-v in` response to predetermined conditions, a balancingl able iinpedances for actuating the saine circuit including afcircular potentiometer adapted to becontinuously energized from said source of pou-er, wiper for said circular potentiometer adapted to'be` moved continuously along the extent of said potentiometer, rotary switching deviceincluding afplurality of stationary contactsand la movable contact, means connecting said adjustable *connections of said sensing cir-cuits to d'staticnary contacts ci said switching means; means-connecting said movable contact v`said switching device to said wiper or" said circular potentiometer, motor means for operating said rotary'switching device and said wiper of said adjustable connections of said plurality of g circuits to said balancing circuit sequenpotentiometer and at varying positions t e'extent of said circuit oi the potentiomr, anti exhibitor means included in said further means responding to a condition determined by .iepassng ci said wiper of said circular potentiometer over a position of electrical potential on potentiometer equal to the electrical potential existing at the respective adjustable connections or"r said vfariable iznpedances of said sensing circuits then connected to said balancing circuit.

8; En device oi' the class described, a plurality oi sensing bridgc circuits each including a pair of adjustable potentiometers, condition responsive means attached to one potentiometer of each, of said bridge circuits for actuating the sarne in response tor a predetermined condition, means connecting said plurality of l bridge circuits together and adapting them to be energized simultaneously from a source of power, and a balancing circuit including a circular continuous potentiometer adapted to be continuously energi/:ed from said source of power, a rotary for said circular potentiometer adapted to be driven continuously along the extent oi said potentiometer, a rotaryswitohing device including a plurality 'of stationary contacts and movable Contact; means connecting one oi' said potentiometers of each of said sensingbridge circuits to said stationary contacts of said switching device, further means connecting 'said movable contact of said switching mined by the passing of the wiper of said circular potentiometer over a `position of electrical potential on said poten'tioineter'equal to an eleclar potentiometer to connect more than one 23 trical potential existing at the respective connections oi said potentiometers of said sensing circuits connected to said stationary contacts then connected to the balancing circuit.

9. In a device of the class described, comprising, a plurality oi sensing circuits each including a variable impedance means having an adjustable connection thereto, means connecting said sensing circuits together and adapting them to be energized simultaneously from a, common` source of power, condition responsive means attached to each of the adjustable connections of said variable impedances for actuating the same in response to predetermined conditions, a balancing circuit including a circular potentiometer adapted to be continuously energized from said source of power, a wiper for said circular potentiometer adapted to be moved continuously along the extent of said potentiometer, a rotary switching device including a plurality of stationary contacts and a movable contact, means connecting said adjustable connections of said sensing circuits to said stationary contacts of said switching means, further means connecting said movable contact of said switching device to said wiper of said circular potentiometer, motor means for operating said rotary switching device and said wiper of said circular potentiometer to connect more than one of said adjustable connections of said plurality of sensing circuits to said balancing circuit sequentially in e, single travel of said wiper over said circular potentiometer and at varying positions along the extent of said circuit of potentiometer, and means included in said further means responding to a condition determined by the passing of said wiper of said circular potentiometer over a position of electrical potential on said potentiometer equal to the electrical potential existing at the respective adjustable connections of said variable impedances of said sensing circuits then connected to said balancing circuit, recording means including a continuous belt with two or more marking elements mounted thereon and a chart record, means including said motor means for driving said belt and said chart record, said belt moving transversely of the movement of said chart record over a predetermined limited distance as each of said sensing circuits is connected to said balancing circuit to dene a channel on said chart record for each sensing circuit which channels do not overlap with respect to one another, one of said marking elements moving relative to said chart record during each switching operation of said switching device, and means for marking said chart record operated by said means included in said further means as it responds to the condition of equal potential in said sensing and balancing circuits.

10. In a device of the class described, in combination, a plurality of sensing circuits each including a potentiometer having a wiper, condition responsive means attached to said wipers for actuating the same in response to a predetermined condition, means connecting said sensing circuits together in a parallel relationship and adapting them to be energized from a source of power, a balancing circuit including a circularl potentiometer adapted to be continuously energized from said source of power, a rotary wiper for said circular potentiometer adapted to be driven continuously along the extent of said potentiometer, a switching device including a plurality of stationary contacts and a movable contact, means connecting said wipers of said potentiometers of said sensing circuits to said stationary contacts of said switching means and said movable contact of said switching device to said wiper of said circular potentiometer to form a plurality of output circuits the outputs of which vary in magnitude and sense, motor means for operating said switching device and said wiper of said circular potentiometer to connect each of said wipers of said potentiometers of said plurality of said sensing circuits to said balancing circuit sequentially and at varying positions along the extent of said balancing potentiometer, relay means included in said second named connecting means having a pair of relays with associated time delay means, said relays being independently operated by said output circuits depending upon the magnitude and sense of output of each of said circuits, means including said time delay means for causing one of said relays to remain operative as the other relay becomes operative upon a change in magntude and sense in the output of said output circuits, and means controlled by the operation of both of said relays.

11. In a device of the class described, in combination, a plurality of sensing circuits each including variable impedances having adjustable connections thereto, means connecting said sensing circuits together in a parellel relationship and adapting them to be energized simultaneously from a source of power, condition responsive means attached to said adjustable connections of said sensing circuits for actuating them in response to a predetermined condition, a balancing circuit including a potentiometer adapted to be continuously energized from said source of power, a wiper for said potentiometer adapted to be moved continuously along the extent of said potentiometer, a switching device including a plurality of stationary contacts and a movable contact, means connecting said adjustable connections of said sensing circuits to said stationary contacts of said switching device and said movable contact of said switching device to said wiper of said balancing potentiometer to form a plurality of output circuits the outputs of which vary in magnitude and sense, motor means for operating said movable contact of said switching device and said wiper of said balancing potentiometer to connect said adjustable connections of said plurality of sensing circuits to said balancing circuit sequentially and at varying positions along the extent of said balancing potentiometer, relay means including a. pair of relays having associated time delay means forming a part of said second named connecting means, said relay means being independently operated by said output circuit means depending upon the magnitude and sense of the output of said output circuits, means including said time delay means causing one of said relays to remain operative as the other relay becomes operative upon a change in magnitude and sense of output of each of said output circuits, and means controlled by the operation of both of said relays to cause an indication of this change in magnitude and sense in the output of said output circuits.

12. In a device of the class described, in combination, a plurality of sensing bridges each including a pair of potentiometers connected in a parallel relationship with one of said potentiometers being operated by a condition responsive means in response to a predetermined condition, means for energizing each of said bridge circuits including a potential dividing means connected across said bridge circuits, a

.balancing circuit including a circular vpotentiometer and a transformer having a tapped secondary .winding connected to said circular potentiometerfor energizing the same, a wiper for said circular potentiometer continuously rotated in contact therewith throughout the full extent or said potentiometer, means connecting pairs of said bridge circuits at one of said potentiometers thereof-to said taps of said secondary winding of said transformer, a rotary switching device having a plurality of stationary contacts and a movableI contact to associate it therewith, means connecting` said bridgecircuits at the other of said potentiometers tosaid stationary contacts, further means connecting said wiper' of said circular potentiometer and said movable contact of said switching device to complete a plurality of output circuits between said bridge circuits and said. balancing circuit, the outputs of which vary in magnitude and sense, motor means actuating said lmovable contact and said wiper of said circular potentiometer to connect more than one of said output circuits during a single travel of said wiper along the extent of said circular potentiometer, and means included in said further means becoming operative when the output of each of said output circuits changes in magnitude and sense.

13. In a device of the class described, in combination, a plurality of sensing circuits each including a potentiometer having an adjustable wiper, condition responsive means attached to said Wipers for actuating the same in response to predetermined conditions, a balancing circuit including a circular potentiometer adapted to be continuously energized from a source of power, means connecting said plurality of sensing circuits together and to said balancing circuit, a rotary wiper for said circular potentiometer adapted to be driven continuously along the extent of the same, a rotary switching device including a plurality of stationary contacts and a. movable contact, means connecting said wipers of said sensing circuits to said stationary contacts of said switching device, further means connecting said movable contact of said switch.- ing device and said wiper oi said circular potentiometer, motor means for operating said rotary switching device and said wiper' of said circuit potentiometer to connect each of said wipers of said plurality of sensing circuits to said balancing circuit sequentially at varied positions along the extent of said balancing potentiometer, means included in said further means responding to a condition determined by the passing of said wiper ci said circuit potentiometer over a position of the electrical potential on said potentiometer equal to the tential existing at the respective wipers of the potentiometers of the sensing circuits then connected to said balancing circuit, and additional potentiometer means connected to said sensing circuits 'for varying the voltage applied to the same.

le. Electrical apparatus of the class described comprising `in combination, circuit means having an output which varies in magnitude and phase, relay means including a pair ci relays each having associated time delay means connected thereto, means including a pair of discriminating connected to said circuit means and said relay means and selectively operative in response to the output of said circuit means depending upon the phase of said output for controlling the operation of one or the other oisaid relays-means including said time delay means causing one of said relays to remain operative while its associated discriminating means becomes inoperative and as the other relay becomes operative upon operation of its associated discriminating means on a change in phase of said output ci said circuit means, and means controlled by the simultaneous operation of both of said relays.

15. Electrical apparatus of the class described comprising in combination, circuit means having an output which varies in magnitudeand phase, relay means including a pair of relays each having associated time delay meansI connected thereto, means including'a pair of discriminating means connected to such circuit means and: said relay means and selectively operative in response to the output of said circa-.it means depending upon the phase of said output for controlling the operation of one or the other of said relays, means including said time delay means causing one of said relays to remain operative while its associated discriminating means becomes inoperative and as the other relay becomes operative upon operation of its associated discriminating means on a change in phase of said output of said circuit means, contact means included in each of said relays and connected in a series relationship, and means connected to said series contacts of said relays and controlled by the simultaneous operation of both of said relays to cause an indication of this change in phase in the output of said circuit means.

16. In a device of the class described, comprising in combination, circuit means having a plurality of combinations each of which has a separate output which varies in phase, rela-y means including a pair of relays each of which includes associated time delay means connected thereto, a pair of discriminating means connected respectively to said pair of relays, switching means sequentially connecting said circuit means to said pair of discriminating means in a plurality of different connections such that said plurality of combinations of said circuit means having different outputs are connected respectively to said pair of discriminating means for each connection, one or the other of said discriminating means being operable in response to the change in phase of the outputs of said circuit means to control respectively the operation of one or the other of said relays, said time delay means causing one of said relays to remain operative as the other of said relays becomes operative on a change in phase of the output for each combi nation of said circuit means, and means controlled by the simultaneous operation of both of said relays each time the output of one of said combinations of said circuit means changes phase.

17. in a device of the class described, comprising in combination, circuit means having a, plurality of combinations each of which has a separate output which varies in phase, relay means including a pair of relays each of which includes associated time delay means connected thereto, a pair of discriminating means connected respectively to said pair of relays, switching means sequentially connecting said Circuit means to said pair of discriminating means in a plurality of lduif-:rent connections such that said plurality of combinations of said circuit means having diierent outputs are connected respectively to said pair or discriminating means for each c-onnection, one or the other of said discriminating ,mea-ns being operable in response to the change 27 in phase of the outputs of said circuit means to control respectively the operation of one or the other of said relays, said time delays means causing one of said relays to rem-ain operative as the other of said relays becomes operative on a change in phase of the output for each combination of said circuit means, means controlled by the simutaneous operation of both of said relays each time the output of one of said combinations of said circuit means changes phase, and means controlled by said last-named means for indicating this change in phase in each of the outputs of said combinations of said circuit means.

ROMAN C. RUHLAND.

28 REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,291,351 Alexander Jan. 14, 1919 2,278,919 Erickson et al. Apr. 7, 1942 2,306,391 Keinath Dec. 29, 1942 2,340,880 Keinath Feb. 8, 1944 y 2,368,953 Walsh Feb. 6, 1945 2,387,760 Keinath Oct. 30, 1945 2,412,092 Mayle Dec. 3, 1946 2,437,242 Cole et al. Mar. 9, 1948 2,460,055 Wilson et a1 Jan. 25, 1949 

